Abstract: In a vehicle seat, a gas generating device of a side airbag apparatus is attached to the inside of an outer side frame in a seat-width direction. When a seated occupant is a three-dimensional mannequin of AM50, a portion of the gas generating device overlaps a back pan of the three-dimensional mannequin as viewed in a seat front-rear direction. Here, in a plan section of a seat back in a range in which the gas generating device is positioned in a seat up-down direction, when an imaginary line overlapping a section of the back pan is moved back toward a seat rear side until the imaginary line comes into contact with a side spring portion of a seat back spring, the gas generating device is positioned rearward of a moved-back imaginary line in the seat front-rear direction and outward of the moved-back imaginary line in the seat-width direction.

Abstract: In a vehicular seat installed with a side airbag device, an inside bag completes inflation and deployment earlier than a side air bag body, on the inner side of the side airbag body in the vehicle width direction, and presses an occupant inward in the vehicle width direction. The inside bag inflates and deploys at an upper level than the abdominal region of the occupant. Further, reaction force is applied inward in the vehicle width direction from a reaction force plate supported by an outer side frame, to the inside bag. The reaction force plate extends in a vehicle front-back direction, and extends toward the front of the vehicle beyond a front edge portion of the outer side frame.